16 January 2004
16 January 2004
The viability of a reusable launch vehicle got a major technological boost recently when Northrop Grumman Corporation delivered the first composite fuel-tank structure to be made without using an autoclave.
The new manufacturing process, which offers the promise of fuel tanks 10 to 25 percent lighter than comparably sized single-use aluminum tanks, would enable heavier payloads and lower operating costs for reusable space vehicles.
Northrop Grumman Integrated Systems delivered one-half of a 10.5-foot diameter composite fuel tank to NASA's Marshall Space Flight Center, Huntsville, Ala., on Oct. 10. The half-tank was produced as part of a contract option under NASA's Next Generation Launch Technology program, an effort to develop and mature technologies required for a next-generation reusable launch vehicle.
""Producing the half-tank taught us a lot about this non-autoclave process and convinced us that we could scale it up to produce significantly larger and very reliable composite fuel tanks,"" said Tod Palm, Northrop Grumman's cryogenic fuel tank project leader.
NASA's vision for a reusable launch vehicle calls for a tank up to 27.5 feet in diameter and 80 feet long. The tanks would be used to store liquid hydrogen, an essential but highly volatile fuel used in the combustion process that propels rockets.
According to Palm, the next phase of tank development will involve refinement of non-destructive techniques for evaluating the quality of the half-tank manufacturing process.
""This tank is not a structural test article but rather a demonstration structure, so we included in its construction an area of intentional, known defects called a standards panel,"" he explained. ""We'd like to see how good our quality-control processes are at detecting and identifying these defects. We'd also like to see how good our processes are at finding any unknown defects.""
Northrop Grumman will use two types of non-destructive evaluation techniques to examine the workmanship of the half-tank: thermography and laser shearography. The company will evaluate both techniques for potential future use in manufacturing large reusable composite fuel tanks.
Thermography flashes infrared energy on a composite structure, then uses a heat-sensing video camera to create a thermal ""map"" of the structure. By analyzing consecutive thermography images, engineers can trace the flow of heat through the part. Defects in the composite material will show up as visual ""irregularities.""
Laser shearography involves scanning the surface of the composite part with a laser, imparting a mechanical load or strain on the part, and then scanning the surface again. Any discontinuities or defects in the composite material, such as an improper bond between the face sheet of the tank wall and its internal honeycomb structure, will show up as a ""bubble"" or other visual distortion.
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